Papers by Author: Kazuyoshi Uematsu

Abstract: Red-emitting RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors were synthesized by a conventional solid-state reaction method, and crystal structure and photoluminescence properties were investigated in the detail. RbLa₂Ti₂TaO₁₀ has tetragonal structure with a space group of P4/mmm, in which the B-site cations (Ta and Ti) are arranged into non-ordering sequence. The RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors exhibited strong red emission, which is due to the 4f-4f transitions of Eu³⁺, at excitation wavelength of 396 nm. The concentration quenching phenomena for RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors was investigated using percolation model with two-dimensional interactions among the Eu³⁺ sites in the host lattice. Both the critical concentration values with the calculation and experiment are estimated to be x = 0.3-0.4, which indicates that the concentration quenching for RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors was due to the energy transfer between the nearest Eu³⁺ ions in these compounds

Abstract: We report novel soft chemical synthesis method, solid hydratethermal reaction (SHR) method as a new soft chemistry. This method is very simple and can synthesize the ceramic materials just by storing the mixture of raw materials added a small amount of water in a reactor at low temperature below 373 K. For example, nanosize YVO₄ (under 100 nm in diameter) was obtained using the SHR method.

Abstract: We succeeded in the single crystal growth of Ba₂SiO₄:Eu²⁺ by novel synthesis method which was gas (SiO) and solid (Ba - Sc - Al - Eu - O) phase hybridized. The Ba₂SiO₄:Eu²⁺ single crystal was synthesized by interfacial crystal growth after the reaction of the SiO gas with the surface of Ba - Sc - Al - Eu - O substrate in the reductive atmosphere. The single crystals were plate-like crystals with about 500 μm sizes and emitted green light around 500 nm under 300 - 450 nm excitation.

Abstract: Anatase TiO₂ having high temperature stability and specific surface area was synthesized using a gel precursor in very mild conditions. The precursor gel was obtained by dialysis treatment of Na₁₆Ti₁₀O₂₈–HNO₃ solution. The samples were characterized by X-ray diffraction analysis, transmission electron microscopy, Brunner–Emmett–Teller method for specific surface area measurements, and thermogravimetric analysis.

Abstract: Photocatalysts for overall water splitting have great potential in solar energy applications. A variety of photocatalysts have shown activity for water splitting. In particular, oxysulfides are the great interest because of their ability to generate H2 and O2 from water under visible light. However, they are generally synthesized under H2S flow, which is an extremely harmful gas for humans. In this study, La2O2S2 was synthesized at low temperature without H2S gas, and its photocatalytic activity was confirmed by hydrogen generation experiments.

Abstract: Low-dimensional structure compounds as layered perovskite shows high photocatalytic activity in water splitting. In this study, we investigated that synthesis and characterization of photocatalytic activity of BaGeGa6O12 with a one-dimensional structure. BaGeGa6O12 with loading 0.3wt% RuO2 showed a photocatalytic activity for water splitting into H2 (70.6 μ mol / h) and O2 (28.1 μ mol / h).

Abstract: We report the synthesis and photocatalytic activity of CaZnGe2O6, which contains Ca2+ ions and one-dimensional GeO4 chains (Ge4+: d10 electronic configuration). This sample demonstrated the water splitting phenomenon by loading with RuO2 cocatalysis. Moreover, Ln-doped CaZnGe2O6 (where Ln = La, Ce, Pr, Nd, or Sm) shows a higher photocatalytic activity than CaZnGe2O6.

Abstract: We synthesized Sr0.7La0.2[ ]0.1Bi2Ta2O9 (SBTL , [ ] vacancy), and measured their photocatalytic activity for water decomposition under UV light irradiation after acid treatment. They showed the high photocatalytic activity under UV light irradiation (H2 evolution (213μmol / h) , O2 evolution (82μmol / h)).

Abstract: Photochemical splitting of water into H2 and O2 using solar energy is process of great economic and environmental interest. In this study, we investigated novel photocatalytic compound, Na16Ti10O28, for water splitting. Na16Ti10O28 was prepared by solid-state reaction at 900 oC for 1 h. Prepared sample was characterized using powder X-ray diffraction, diffuse reflectance spectrum, and scanning electron microscopy. As-prepared Na16Ti10O28 sample is easily hydrated in water. Hydrous Na16Ti10O28 showed H2 evolution without co-catalyst.

Abstract: Fine TiO2 particles were synthesized from titanate precursor, Na16Ti10O28, dissolved in aqueous HNO3 solution. Crystalline rutile TiO2 powders were prepared by reflux of dissolved powders in the aqueous HNO3 solution under 100 °C. Prepared TiO2 powders were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy and BET specific surface area analysis.